CROSS‐MODAL PERCEPTION IN APES *

I should like to describe some experiments in cross-modal perception with apes and monkeys and to attempt to relate this phenomenon to the origins of speech and language. The sensory modalities of most human adults operate in concert as an integrated system of systems. Information received via one modality is coordinated in some manner with information from other modalities, and much of adaptive behavior, including language, presumably depends to a large extent on this intermodality integration. The existence of cross-modal perception and the unity of the senses in humans was graphically testified to by von Hornbostel when he said, “It matters little through which sense I realize that in the dark I have blundered into a pigsty.”’ In routine activities, we are seldom aware of the marked discrepancies in information originating in the several sensory modalities. The extent to which this capacity is shared with psychologically and neurologically unusual humans, infants, and other animals is not entirely clear. The interrelatedness of the senses, variously termed intermodal or cross-modal transfer, intermodal integration or generalization, cross-modal perception. and the like has a long philosophical history, extending a t least as far back as the early 1700s with Locke and Berkeley, but a relatively brief clinical and experimental history. Neurological case studies of the late 1800s provided some interesting data, and von Senden’s observations published in 1932 on early-blinded people whose sight was restored in adulthood were more directly relevant. Experimental work with humans, including the blind, deaf, neurologically damaged, very young children, and normal adults, has accelerated in the past few years (see reviews by Freidesz and Gibson3). Experimental investigations with nonhuman animals aimed directly a t cross-modal perception are recent and still rather few in number. There are a number of fundamental issues regarding cross-modal perception which require clarification: I . What are the roles of maturation and experience in its expression? 2. What are the neurological requisites for the phenomenon and in what manner d o neuroanatomical characteristics facilitate cross-modal perception (in part a phylogenetic issue)? 3. What is the nature of the information processing that permits integration of information among the several modalities? 4. To what extent d o other behavioral capacities such as language mediate or facilitate perceptual integration? 5 . To what extent d o cross-modal capabilities contribute to adaptive behavior in general, and cognitive processes and language in particular? 6. In what manner and to what extent d o intramodality characteristics or limitations in and of themselves contribute to cross-modal functioning?